1. Field of the Invention
The present invention is directed generally to a printer or copier using a toner that is fixed on a carrier and in particular to a fixing station for fixing toner images on a carrier material, comprising a heating device having at least one heat emission source that emits radiation in the direction of the carrier material, and comprising a cover with which undesired incidence of radiation onto the carrier material can be prevented.
2. Description of the Related Art
In electrographic printers or copiers, the toner image transferred from an intermediate carrier, generally a photoconductor, onto the carrier material, which is generally paper, must be fixed, i.e. it must be connected to the carrier material so as to be smear-proof and abrasion-resistant. Heat-pressure fixing is usually utilized at present in electrophotography. When no pre-heating of the carrier material is undertaken, which may ordinarily be done for example with the assistance a heating saddle, this heat-pressure fixing is limited in processing speed to approximately 0.5 m/s through 0.7 m/s. In a duplex printing mode wherein the front side and the back side of a carrier material is printed, the fixing process is relatively difficult since both sides are provided with toner images that can still smear. A high toner fixing quality given simultaneous fixing of the front side and of the back side of the carrier material can only be achieved with relatively soft fixing drums, for example silicone drums. These fixing drums have a short surface life and are uneconomical. Such soft fixing drums are therefore utilized only in printers having a relatively low printing volume. Since soft fixing drums are utilized at both sides of the carrier material, the guidance of the carrier material is problematical. Such fixing drums are therefore not suited for the further-processing of continuous form paper.
For these reasons, it is desirable to fix toner images in as contact-free a manner as possible, whereby a relatively broad spectrum of carrier material can be utilized. A further goal of contact-free fixing is comprised in achieving a high toner fixing quality without smearing effects.
A contact-free fixing method is known wherein the toner material is softened with the assistance of a solvent so that it unites better with the fibers of the carrier material. When, however, chromatic toner is employed, it can occur that the color pigments are dissolved to different degrees, which can lead to a far-dependent smearing of the toner images. Moreover, the known environmental problems given the employment of solvents arise.
Another known fixing method that works in a contact-free manner is what is referred to as photoflash fixing, whereby the toner is fixed on the carrier material with the assistance of high-energy light pulses. The wavelength of the radiation usually lies in the visible light through ultraviolet range of the spectrum. Since the different chromatic toners absorb the radiation to different extents in this wavelength range, photoflash fixing is not suitable for multicolored printing.
A further fixing station is disclosed by European Patent Document EP-A-0 629 930. The fixing station is used for an electrostatic printer in order to fix the toner material on paper. A cover device serves the purpose of preventing the incidence of radiation during a warm-up phase or during a standstill of the carrier material. In the closed condition of the cover device, the active surfaces of the heat emission source that emit heat radiation face away from the carrier material. In this condition, the cover device surrounds the heat emission source, so that the warm-up phase is shortened. During normal operation wherein the toner material is fixed on the carrier material as a result of the incident heat radiation, the heat radiation source faces toward the carrier material and radiation can impinge the carrier material unimpeded.